Create README with grammar spec

README

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+                             REGEX ENGINE
+
+I've thought for a while it would be fun and interesting to write my
+own regular expression engine using Thompson's construction algorithm,
+so here we are.
+
+                               Grammar
+
+This engine is not going to be strictly supporting any standard
+syntax; the expression syntax I intend to support follows.
+
+	regex ::= sequence ( '|' regex )?
+	sequence ::= term+
+	term ::= ( '.' | class | literal | '(' regex ')' ) quantifier?
+	class ::= '[' '^'? literal+ ']'
+	literal ::= non-special | '\' special
+	quantifier ::= '*' | '+' | '?'
+	special ::= quantifier | '|' | '(' | ')' | '[' | ']' | '^' | '\'